A138598 Numbers k such that 2^(2*k-27)-27 is prime.

16, 17, 23, 25, 305, 1277, 2675, 3179, 8987, 9013, 27493, 42703

Offset

1,1

Comments

a(14) > 10^5. - Michael S. Branicky, Sep 13 2024

Links

Table of n, a(n) for n=1..12.

Example

2^(2*17-27)-27=101, 2^(2*23-27)-27=524261, 2^(2*25-27)-27=8388581, ...

Mathematica

q=27; For[i=q, i<=q, a={}; Do[x=2^(2*n-i)-i; If[PrimeQ[x], AppendTo[a, n]], {n, 20^2}]; Print["2^(2*n-", i, ")-", i, " ", a]; i=i+2]
Select[Range[1000], PrimeQ[Abs[2^(2#-27)-27]]&] (* Harvey P. Dale, Nov 12 2015 *)

Prog

(PARI) is(n)=ispseudoprime(abs(2^(2*n-27)-27)) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Sequence in context: A007636 A241751 A374559 * A244431 A151977 A252492

Adjacent sequences: A138595 A138596 A138597 * A138599 A138600 A138601

Keyword

more,nonn

Author

Vladimir Joseph Stephan Orlovsky, May 13 2008

Extensions

a(7)-a(11) from Iain Fox, Jan 13 2018

a(12) from Iain Fox, Jan 16 2018

a(13) from Iain Fox, Jan 18 2018

15 removed by Sean A. Irvine, May 21 2026

Status

approved